In LEDs and optical semiconductor devices, a transparent resin is commonly used as a sealing material of a light emitting element. Examples of the transparent resin include epoxy resins and silicone resins of the addition curing type, condensation curing type, and UV curing type. Silicone resins are particularly used for sealing high-luminance and high-output optical semiconductor elements (e.g., white LED) because they form cured products having excellent properties such as weather resistance and heat resistance. The silicone resins however have poor adhesion to noble metals (e.g., silver) which are used as semiconductor materials. Moreover, the silicone resins also have poor adhesion to polyphthalamide resin (PPA), which is a reflector material. Depending on heat radiation from the light emitting element and the temperature cycle, the adhesion further lowers to problematically cause separation between a base material (e.g., PPA) or a noble metal electrode and the silicone resin.
To solve such problems, adhesion-imparting agents such as various silane coupling agents are added to improve the adhesion. The effect thereof is, however, not sufficient. Moreover, such a composition disadvantageously has its adhesion lowered due to very high moisture absorption, leading to poor durability.
Patent Literature 1 discloses an addition-curable silicone resin composition containing an isocyanuric ester having an epoxy group as an adhesion-imparting agent. Patent Literature 2 discloses, as an adhesive silicone resin, a reactive modified silicone resin containing vinyl and carbamate groups in the same molecule and having an alkoxy or OH group bonded to a silicon atom at one molecular end.
However, a means of adding an isocyanuric ester as disclosed in Patent Literature 1 does not give a sufficient effect of improving the adhesion to a base material.
A modified silicone resin as disclosed in Patent Literature 2 includes a vinyl group that provides curability and a carbamate group that provides adhesion in the same molecule. In this case, carbamate groups may be uniformly dispersed in the entire cured resin and the concentration thereof around the adhesion interface may lower, possibly resulting in an insufficient effect of improving the adhesion. Moreover, if the amount of carbamate groups in molecules is increased to increase the concentration of carbamate groups around the adhesion interface, physical properties or durability of the silicon resin may be adversely affected.
In addition, a silicone resin containing an alkoxy or OH group bonded to a silicon atom problematically has poor storage stability.